This invention relates to a device for picking-up a part from a first manufacturing station and thereafter placing and releasing the part in a second station. Such devices are typically used in robotics and automatic manufacturing applications and are commonly referred to as xe2x80x9cpick and placexe2x80x9d devices or xe2x80x9ctransfer mechanismsxe2x80x9d.
Pick and place devices known in the art typically incorporate two axes of motion configured perpendicular to each other. For example, two independently operated pneumatic slide carriages can be mounted on axes perpendicular to each other, wherein the first carriage supports the second carriage. The two carriages can be driven either by linear servo motors or by ball screws and rotary servo motors. An example of such a two-axes, two-carriage device is illustrated in U.S. Pat. No. 5,086,559 to Akatsuchi.
The disadvantage of such prior art devices is that the first carriage axis carries the second carriage axis. Therefore, the first axis must robust enough to carry the weight of the part being moved in addition to the weight of the second axis, and the driving force propelling the first axis must be large enough to accelerate and decelerate the part in addition to the second axis. Another disadvantage is that the accuracy of the motion of the second axis depends on the accuracy of the mounting that attaches the second axis to the first axis. If the two axes are not mounted exactly perpendicular to each other, the motion will not have the desired accuracy. Moreover, the mounting is often fixed during manufacturing and cannot be adjusted in the field.
Instead of using two independently powered carriages on two perpendicular axes, some pick and place devices utilize a barrel cam driven by an electric motor, or a pneumatic cylinder moving the carriages in a cam slot. Pick and place devices utilizing U-shaped cam slots are illustrated in U.S. Pat. No. 5,564,888 to Doan, and U.S. Pat. No. 4,740,134 to Dixon. A pick and place machine utilizing a generally Y-shaped cam slot is illustrated in U.S. Pat. No. 4,451,196 to Harada et al.
A primary disadvantage of these cam-type prior art devices is that they provide little, if any, provision for adjustment of the device motion ranges. Typically, the motion of the device is fixed, thereby requiring that the parts handling system be built around the dimensions of the pick and place device. If the pick and place device does not have the exact range of motion specified by the manufacturer, the parts handling system must subsequently be redesigned.
Using another type of transfer apparatus, U.S. Pat. No. 3,065,861 to Cruciani discloses a rope crane having substantially parallel carrying ropes with a pair of blocks connected to one another. By winding the rope of one capstan and paying out the rope of another capstan, the pair of blocks can be carried to any desired point located between two predetermined locations. The main disadvantage of this rope crane is that, since it relies on gravity, it can only exert a positive force in the upward direction (i.e., a xe2x80x9cpull forcexe2x80x9d), and cannot exert a positive force in the downward direction (i.e., a xe2x80x9cpush forcexe2x80x9d). The inability to provide a positive pushing force prohibits the device from operating effectively as a pick and place device, particularly if the device is inverted (e.g., located under the automation system).
U.S. Pat. No. 4,687,400 to Lichti discloses another type of device for moving objects in a closed container. This complex device has four degrees of freedom (i.e., up-and-down, back-and-forth, opening and closing the fingers, and rotation around a horizontal axis) but requires manipulation of four arms to obtain the desired motion. Linear horizontal motion is complicated as it requires a combination of vertical and rotational motion. Therefore, it is too complex and expensive for cost-effective use in an application requiring only two degrees of freedom (i.e., up and down, side-to-side).
U.S. Pat. No. 4,190,912 to Nilsson discloses a device for lifting and transferring a hospital patient. Rotation of a lever, pivotally attached to a connecting rod at a predetermined angle, raises, translates, and then lowers a patient in and out of bed. However, due to its design, the range of vertical movement is fixed through the entire lift and transfer cycle (i.e., the mechanism must place at the same level it picks). Thus, this mechanism can-only move from a first predetermined location to another predetermined spot at approximately the same height as the first location, and has limited flexibility.
A need, therefore, exists for a two-axis pick and place device that is simple in construction, highly accurate, programmably adjustable, robust in operation, and yet cost effective.
Accordingly, it is a primary object of the present invention to provide a pick and place device which overcomes the disadvantages previously described.
It is another object of the present invention to provide a pick and place device that can be programmed to move in accordance with the computer instructions of many different manufacturing operations.
It is still another object of the present invention to provide a pick and place device that has carriages which move along two parallel axes instead of two perpendicular axes, to increase the accuracy of movement.
In accordance with one aspect of the present invention, there is provided a pick and place device comprising a single elongate frame extending in a longitudinal direction, first and second carriages slidingly engaged on the frame, first and second motors which drive each of the first and second carriages to slide along the frame, a gripper for gripping an object to be relocated, a first linking arrangement including at least two connecting rods pivotally attached to the first carriage at one end and pivotally attached to the gripper at the other end, and a second linking arrangement including at least one connecting rod pivotally attached to the second carriage at one end and pivotally attached to the gripper at the other end.
In accordance with the present invention, the method of picking and placing an object includes the steps of sliding the first and second carriages away from each other along the frame substantially simultaneously in opposite directions which moves the gripper in an upward direction, sliding the first and second carriages along the frame substantially simultaneously in the same direction which moves the gripper in a lateral direction, and sliding the first and second carriages toward each other along the frame substantially simultaneously in opposite directions which moves the gripper in a downward direction.
In accordance with another aspect of the present invention, there is provided a pick and place device including carriages slidingly engaged with a frame, a platform with an attached gripper, and at least four connecting rods extending between the platform and the carriages, the platform having a first range of motion in a first direction and a second range of motion in a second direction that is substantially perpendicular to the first direction. The first range of motion depends on the length of the frame and the length of the connecting rods. The second range of motion depends on the length of the frame only.
In accordance with still another aspect of the present invention, there is provided a pick and place device comprising an elongate frame extending in a longitudinal direction, a first carriage assembly slidingly engaged with the frame and including at least two pivotally mounted connecting rods, a second carriage assembly, operatively independent from the first carriage assembly, slidingly engaged with the frame and including at least two pivotally mounted connecting rods, a platform pivotally connected to the connecting rods of the first and second carriage assemblies, and a motor which drives each of the first and second carriage assemblies to slide along the frame. Sliding the carriage assemblies along the frame away from each other exerts a force to move the platform in a first direction. Sliding the carriage assemblies along the frame in the same direction exerts a force to move the platform in a second direction which is substantially perpendicular to the first direction. Sliding the first and second carriage assemblies along the frame toward each other exerts a force to move the platform in a third direction, substantially opposite to the first direction.